With the advent of vertical retreat mining methods, corresponding new in-the-hole ("I-T-H") drilling units are being introduced. As the technology has progressed, there has been a decided push to automate and otherwise improve current and newly developed I-T-H drills.
It is conventional practice to fabricate drill string components such as pipes, hammers, etc. with wrenching slots. Accordingly, I-T-H percussion hammers usually have a chuck part (or bottom hammer subassembly) slotted for a fork-table wrench. In this fashion, in order to attach or detach the hammer from the bit the wrench is slipped over the flats of the slot of the hammer to either make or break the connection with the stem of the bit.
By virtue of the current slotted design of the hammer, the process of slotting the flats cuts through the outer case hardened surface of the hammer which ultimately causes premature wear. Moreover the constant extension and retraction of the wrench ultimately causes the flats to strip and wear out thereby making it more and more difficult to attach/detach the hammer from the bit. Ultimately the exterior of the worn hammer must be remachined or if that fails, the entire unit disposed of.